Analysis and solution of erosion failure in drill pipe thickening transition zone

• The causes of the leakage in the transition zone of the thickened drill pipe are investigated and studied.
• The drill pipe leakage is due to the drill pipe screen with a straight cylinder structure placed in the drill pipe, which is also the main cause of drill pipe erosion. In order to solve the erosion of the drill pipe screen on the inner wall of the drill pipe, a conical drill pipe screen can be placed in the anti-protection joint at the lower part of the Kelly.
• For the top drive drilling rig, the conical drill pipe screen is placed in the short joint between the hose and the tap. The erosion failure of drill pipe thickening transition zone is avoided, so as to ensure the reliability of drill pipe and meet the needs of drilling production.

When drilling in an area with a complex geological environment, drill pipe leakage often occurs
However, some drill pipes even the inner coating didn’t fall off, which caused a lot of economic losses.
Through field investigation, it is found that in the construction of horizontal and inclined wells, in order to filter impurities and foreign matters in drilling fluid and avoid damage to directional instruments, a tubular porous drill pipe screen is placed on the threaded end of the drill pipe, which leads to frequent erosion failure in the transition zone of thickening of drill pipe.

The main feature of drill pipe erosion failure is that the high-pressure drilling fluid containing solid particles impacts the inner surface of the drill pipe thickening the transition zone at a high speed along a certain direction, resulting in the loss of metal.
The most common ones are erosion pits, erosion holes on the surface of the thickened transition zone in drill pipe, and erosion of thread and sealing surface caused by erosion of thread connection.

When a drill pipe screen is installed in the drill pipe, the flow direction of the drilling fluid changes suddenly, from parallel to the inner wall of the drill pipe to directly shoot into the inner wall of the drill pipe. The drilling fluid ejected from the water hole of the drill pipe screen shoots into the inner wall of the drill pipe at high speed. This kind of jet erosion is equivalent to “jet drilling” in drilling engineering. In material science, this kind of damage pattern is called “erosion”.
It results in peeling off of the inner coating and further aggravation of corrosion. There is a bulge in the round erosion pit due to the repeated impact of drilling fluid. The reason is that there is a stagnation point in the jet center and the flow velocity is low.
With the deepening of the pit, the flow direction of drilling fluid in the string changes, the bulge gradually moves up, and the downstream edge of the pit gradually flattens, forming a horseshoe-shaped pit.
After the drill pipe is corroded, cracks are generated, and the cracks gradually expand in the process of use. The erosion pits are subject to fatigue fracture and leakage under the combined action of alternating stress and corrosion.

Tapered drill pipe screen

Based on the analysis of the existing drill pipe screen, the conical drill pipe screen is developed, and the big end of the drill pipe screen is lengthened by 80mm, so that the drill pipe screen can not be used in the drill pipe, and can only be used in the matching new type anti protection joint.
At the same time, the jet angle of the mud to the inner wall of the drill string changes from a certain angle to the inner wall of the drill string.

Characteristic：

• The conical drill pipe screen is equipped with an extension joint, which can only be used in pairs but can not be placed in the drill pipe to meet the requirements of drilling fluid filtration in directional drilling.
• The cone filter tube can increase the annulus volume, prevent the pump pressure from rising and improve the hydraulic parameters of drilling.
• Stainless steel is used to process the body and sandblast the inner and outer surfaces to improve reliability and prolong the service life.

Conclusion

• By changing the drill pipe screen from the original straight cylinder shape to the cone shape, the flow direction of the drilling fluid changes from the vertical injection to the inner wall of the drill string at a certain angle, which improves the hydraulic efficiency of the drilling fluid and reduces the erosion of the drilling fluid on the inner wall of the drill string.
• According to the structure of the drill pipe screen, the matching joint is processed to completely avoid erosion damage to the drill pipe. The length of the joint is 1.22m and the wall thickness is 41.25mm, which is much larger than the wall thickness of the drill pipe of 9.19mm and can resist the erosion of drilling fluid.
• The top end of the drill pipe screen is lengthened by 80mm so that it can not be used in the drill pipe to avoid the accident of the drill pipe screen going down with the drill pipe.
• The drill pipe screen is placed in the short joint between the water hose and the water tap, which solves the problem that the drill pipe screen cannot be placed in the top drive drilling rig, and prevents the drill pipe from leaking in the thickened transition zone.
• The application of the new drill pipe screen device in some oilfields has significantly reduced the drill pipe leakage, improved the service life of drilling tools, reduced the number of tripping operations, and met the needs of drilling speed and efficiency.